1. Field of the Invention
The present invention relates to multilayered LC composite components such as multilayered LC filters and methods for adjusting the frequencies of the composite components.
2. Description of the Related Art
Conventional filters used in a mobile phone and other communications devices include a multilayered LC filter. The multilayered LC filter is a chip-shaped LC composite component formed by laminating internal electrodes including capacitor electrodes and inductor electrodes with dielectric layers. Such a multilayered LC filter is suitable for miniaturization.
On the other hand, in this kind of multilayered LC filter, uniformly setting the frequency characteristics of the filter is relatively difficult. Thus, after manufacturing the filter, frequency adjustments are required to be performed. Specifically, a trimming electrode opposing internal electrodes is first arranged on a surface of the multilayered LC filter, and next, a portion of the trimming electrode is removed via laser, or by sandblasting or some other cutting method, which is referred to as a so-called functional trimming method.
However, since there are limitations to a minimum cutting amount obtained by the cutting method adopted in the frequency adjustment method described above, it is difficult to finely adjust the frequency of the filter.
In order to overcome the problems described above, preferred embodiments of the present invention provide a multilayered LC composite component in which fine adjustments to a desired frequency can be easily and accurately made. Additionally, preferred embodiments of the present invention provide a method for adjusting the frequency of the composite component.
According to a first preferred embodiment of the present invention, a multilayered LC composite component includes a multilayered body having internal electrodes including capacitor electrodes and an inductor electrode which are laminated via dielectric layers, input/output external electrodes and a ground external electrode disposed on a surface of the multilayered body, a trimming electrode disposed on a surface of the multilayered body such that the trimming electrode is opposed to at least one of the internal electrodes and electrically connected to the ground external electrode, an isolated electrode that is separated from the trimming electrode by a trimming groove, and a coating material filled in the trimming groove, the coating material having a dielectric constant that is smaller than the dielectric constant of the dielectric layer.
With the above unique arrangement, the frequency of the multilayered LC composite component can be adjusted to a desired frequency by forming a capacitance between the internal electrodes and the trimming electrode, between the internal electrodes and the isolated electrode, and between the trimming electrode and the isolated electrode. In other words, first, a rough adjustment is made by forming the isolated electrode, which is separated from the trimming electrode, and next, a fine adjustment is made by filling the coating material in the trimming groove, with the result that the frequency of the multilayered LC composite component can be adjusted to the desired frequency.
In addition, in the multilayered LC composite component of this preferred embodiment of the present invention, the isolated electrode may be an insular electrode surrounded by the trimming electrode via the trimming groove. With this arrangement, since variations in a trimming area caused by the positional deviation of a trimming region are reduced, the trimming can be satisfactorily performed.
Furthermore, in the multilayered LC composite component according to this preferred embodiment of the present invention, the coating material may have a dielectric constant between about 1.5 and about 10. In this preferred embodiment of the present invention, since the fine adjustment is performed by applying the coating material, it is preferable that the dielectric constant of the coating material is small. On the other hand, when the dielectric constant is extremely small, the maximum of the varying range is limited. Thus, preferably, the minimum dielectric constant is about 1.5 or greater. In contrast, when the dielectric constant is excessively great, it is difficult to benefit from the effects of the fine adjustment. As a result, preferably, the maximum dielectric constant is about 10 or smaller.
Furthermore, according to a second preferred embodiment of the present invention, a method for adjusting the frequency of a multilayered LC composite component including a multilayered body in which internal electrodes having capacitor electrodes and an inductor electrode are laminated via dielectric layers, input/output external electrodes and a ground external electrode disposed on surfaces of the multilayered body, and a trimming electrode disposed on a surface of the multilayered body such that the trimming electrode is opposed to at least one of the internal electrodes and electrically connected to the ground external electrode, the method including the steps of making a primary adjustment in which trimming groove is formed in the trimming electrode to form the isolated electrode separated from the trimming electrode so that a capacitance between the trimming electrode and the internal electrode is reduced to be smaller than a capacitance for a desired frequency, and making a secondary adjustment in which a coating material having a dielectric constant that is smaller than the dielectric constant of the dielectric layer is filled in the trimming groove to slightly increase a capacitance between the trimming electrode and the isolated electrode so as to adjust to the desired frequency.
As mentioned above, in preferred embodiments of the present invention, the adjustment for obtaining the desired frequency is performed preferably via two steps including the primary adjustment as the rough adjustment and the secondary adjustment as the fine adjustment. That is, first, before the formation of the electrode isolated from the trimming electrode, the one capacitance is present between the trimming electrode and the internal electrode. Then, after the formation of the isolated electrode, two capacitances are generated, that is, the capacitance between the trimming electrode and the internal electrode and the capacitance between the internal electrode and the isolated electrode. This is the primary step for the adjustment forming the two capacitances. Specifically, since the isolated electrode separated by the trimming groove is a floating electrode that is disconnected from the ground external electrode, a potential difference between the isolated electrode and the internal electrode is smaller than a potential difference between the internal electrode and the trimming electrode connected to the ground external electrode. As a result, due to the smaller potential difference between the isolated electrode and the internal electrode, a synthesized capacitance obtained after the isolation is smaller than the capacitance obtained before the isolation. With the primary adjustment, the synthesized capacitance between the trimming electrode and the internal electrodes is temporarily smaller than the synthesized capacitance in which the desired frequency is obtainable.
Next, the secondary adjustment is performed by filling the coating material in at least the trimming groove. In other words, the coating material is applied on the multilayered body to generate a small amount of capacitance between the trimming electrode and the isolated electrode mutually opposing in a surface direction via the coating material. With the secondary adjustment, since the capacitance between the trimming electrode and the isolated electrode slightly increases, a synthesized capacitance obtained from the three capacitances also slightly increases. Thus, the temporarily reduced synthesized capacitance in the primary adjustment can be slightly increased in the secondary adjustment. Consequently, the synthesized capacitance can be closer to the capacitance for the desired frequency.
Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.